Neonicotinoids In Water

Carpenter Bee

Male Carpenter Bee Landing on a Flower

The overuse of neonicotinoids has led to increased levels of enviromental contamination. Several studies have found neonicotinoid contamination in ground water (well water). How does it get there? Two major routes for groundwater contamination are “Point Source” and “Non-Point Source”. Examples of point source contamination include a pesticide directly entering the ground water through and open well or a spill of concentrated chemical that moves as a plume that overwhelms the capacity of the soil to absorb the chemical and the soil microorganisms to degrade it. Non-Point Source pollution is limited to those chemicals that are sufficiently soluble in water, persistant in the soil and a density typically much greater than water. Given the water solubility and density of neonicotinoids (the density of Thiamethoxam is 1.57) neonicotinoids can sink in the water column and continue a downward journey. Once below the biotic zone of the soil, the persistance of a chemical can increase because of lack of metabolism.

Huseth and Groves* studied the movement of neonicotinoids and found that thiamethoxam is capable of moving through a soil lysimeter (column of soil). In experiments in potato fields, they found increased movement of insecticide after the potato vines were killed. This was true for both foliar treatments and timed release soil treatment. In furrow treatments produced the most leachate prior to vine kill. When the vines are killed, neonicotinoid present in leaves may be released to the soil and the root zone moves much less water and insecticide from the soil making more available for leaching. Their study supports non-point source as a contamination mechanism.

Ideally, pesticide contamination is minimized to low levels. This can sometimes be managed with proper formulation or changes in application. This and other studies raise questions about biological impact of these chemicals in ground water.

*Huseth AS, Groves RL (2014) Environmental Fate of Soil Applied Neonicotinoid Insecticides in an Irrigated Potato Agroecosystem. PLoS ONE 9(5): e97081.
doi: 10.1371/journal.pone.0097081

About jjneal

Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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